particle physics and cosmology - university of...

PARTICLE PHYSICSAND COSMOLOGY

Jonathan FengUC Irvine

UCI QuarkNet 21 August 2003

21 August 2003 UCI QuarkNet Feng 2

CONNECTING THE VERY, VERY SMALL WITH THE REALLY, REALLY BIG


Standard Model of Particle Physics

• c. 1970s

• Explains data down to length scales of 10-16

cm


Particle Physics – Experiment

High Energy Colliders

Tevatron


Standard Model of Cosmology

• c. 2003

• Explains data up to length scales of 1028 cm


Cosmology – ExperimentSatellites, telescopes

HS

T

Auger

WM

AP

Whipple


Connections – Theory

Why do particle physicists care about cosmology?

Cosmology poses fundamental questions: – What is dark matter? – What is dark energy? – Why is there more matter than anti-matter?

The standard model of particle physics is amazingly successful, but…

It’s missing 96% of the universe, and we don’t understand why the remaining 4% is still here.


Connections – Experiment• Cosmology also provides tools to help answer these

questions– Ultrahigh energy collisions now– Ultrahigh energies from the Big Bang

… for FREE !

• Drawbacks– “Experimental rates” are low – need BIG detectors– Cosmological “experiments” were done a long time ago– Cosmological “experiments” are irreproducible


Cosmic Rays – Past • 1935 Yukawa postulates the pion with mass ~ 100 MeV.• 1937 Anderson discovers the “mesotron” in cosmic rays with

mass ~ 100 MeV.

• 1941-45 WW II.

• 1946 Powell and Occhialini discover pions π− (139 MeV) in cosmic rays. Mesotrons identified as muons µ− (106 MeV).

• 1946 Rochester and Butler discover kaons K0 (494 MeV) in cosmic rays.

• 1948 First man-made pions π− and π0 (134 MeV) produced at Berkeley 184-inch cyclotron.

π− µ−


Cosmic Rays – Present

• Neutrino masses and mixings discovered through cosmic rays at SuperKamiokande in 1998

• Man-made neutrino sources provide evidence for mixings at KamLAND in 2002


Cosmic Rays – Future

• Cosmic rays observed with energy ECR ~ 1019 eV(~ major league fastball)

• For fixed target collisions, the center-of-mass energy is ECM = (2 ECR mp)1/2, so

ECR~1019 eV ECM~100 TeV LHC

SLACB factory

Tevatron

• Higher energies than any man-made collider


Cosmic Rays – Future Black Hole produced here


Dark Matter

disk ends here

inferred

data


Big Bang Nucleosynthesis• What is the halo made of? Not

atoms!

• As the universe cools, protons form nuclei. The number of protons determines the amount of light elements in the universe.

• All light elements agree: protons make up 4% of the universe’s mass, whereas the required amount of halo matter is 29%. The remaining 25% is dark matter.


What is Dark Matter?

• Must be neutral, very long-lived, heavy.

• All known particles are easily eliminated.

• Dark matter is the best evidence that the standard model of particle physics is incomplete, and motivates many extensions.

• Some candidates: – WIMPs (e.g., neutralinos)– Axions


WIMPs

• Among the best candidates so far: weakly-interacting massive particles. These particles have weak interactions only.

• They are produced in the Big Bang, and interact via SM + SM ↔ WIMP + WIMP. As the universe expands, they become diluted, and eventually can’t find each other – they “freeze-out.” Their relic density is determined by their interaction strength.

• WIMPs are automatically left with the right amount to be dark matter.


WIMPs

Exponentialdrop

Freeze out

time

Freeze outSto

ck p

rice

($)

Exponentialdrop

• Universe cools, leaves a residue of dark matter with ΩDM ~ 0.1 (σWeak/σ)

• 13 Gyr later, Martha Stewart sells ImClone stock – the next day, stock plummets

Coincidences? Maybe, but worth investigation!


Supersymmetric WIMPs

Z 0

SU(2)

Hd0

ν1/2

γ1

3/2

Ggraviton

2

Down-typeUp-typeU(1)Spin

Neutralinos: χ≡χ1, χ2, χ3, χ4

Z 0

Zino

Z 0

SU(2)M2

νsneutrino

HdHu0

νHd

HiggsinoH u

Higgsinoγ

Photino1/2

γ1

Ggravitino

3/2

Ggraviton

2m3/2mν

Down-typeµ

Up-typeµ

U(1)M1Spin

Cold Dark Matter WIMP candidates: neutralino, sneutrino


WIMP Detection

WWIIMMPP

CDMS in the Soudan mine ½ mile underground in Minnesota


Axions

• Axions are particles predicted in theories designed to explain why CP violation is so small.

• Axions interact with photons and are very light with masses of µeVto meV.

• However, they interact extremely weakly.


Axion Detection


Dark Matter – Future Collider Inputs

Dark Matter Parameters

χχ Annihilation χN Interaction

Relic Density Indirect Detection Direct Detection

Astrophysical and Cosmological Inputs


Dark Energy

• Cosmology 70% of the mass of the universe is in dark energy (also known as the cosmological constant).


What is Dark Energy?

• Dark energy is the energy stored in a vacuum. From quantum mechanics, recall that an oscillator has energy ω (n ± ½), where ω2 = k2 + m2; ±ω/2 is the vacuum energy. (Set ħ=1.)

• In quantum field theory, we must add up vacuum energies for all wave numbers k. For each particle, we get

±½ ∫Ed3k (k2 + m2)½ ~ ±E4,

where E is the energy scale where the theory breaks down.


Expectations for Dark Energy• We expect E ~ MPlanck ~ 1019 GeV, or at least E ~ Mweak ~

100 GeV. But cosmology tells us E ~ 10-3 eV ! Independent contributions must cancel to incredible accuracy.

• Problems:– Why is ΩΛ so small? – Why is ΩΛ not zero?– Why is ΩΛ ~ ΩM?

• The cosmological constant problems are the most profound problems facing particle physics today. No reasonable solutions. (Anthropic principle?)


Summary• Cosmology provides fundamental questions…

– What is dark matter?– What is dark energy? – Why is there matter and not anti-matter?

• … and fundamental tools for finding the answers– The universe is Nature’s high energy collider

• The big and small are inextricably linked as particle physics and cosmology enter a golden era.


Ouroboros

particle physics and cosmology - university of...

Documents